Bis-.beta.-hydroxyalkyl ethers of halogenated bisphenols are known and are used as hydroxyl components for the production of flame-resistant synthetic resins. These bis-ethers are generally solid crystalline or vitreous (i.e. glass-like) resins. Esters of these ethers with dicarboxylic acids are also known and have been used for the production of flame-resistant synthetic resins. For example, the production of an ester by esterification of bis-.beta.-hydroxyethyl dibromobisphenol and 1,2-propylene glycol with a mixture of phthalic acid anhydride and maleic acid anhydride has been described in Canadian Pat. No. 663,542. This ether contains 25.2% of bromine and is a vitreous resin at room temperature. For producing polyurethane and polyisocyanurate resins, however, it is advantageous to use liquid or low viscosity starting components so that the foaming mixture may be poured.
Polyethers which contain free hydroxyl groups, e.g. polyethylene glycol or polypropylene glycol, have long been used as low viscosity components for producing polyurethane and polyisocyanurate resins. Hydroxyl-containing polyethers of bisphenols are also known for this purpose. It appears from U.S. Application Ser. No. 373,230, filed June 25, 1973, now abandoned, that polyethers of halogenated bisphenols cannot be produced under conventional operating conditions. The treatment of highly halogenated bisphenols, such as tetrabromobisphenol, with alkylene oxides merely results in bis-ethers of the type mentioned above, even when an excess of alkylene oxide is used.
It would be an obvious solution to dissolve these bis-ethers in low-viscosity polyalkylene glycols in order to incorporate them in the foaming mixture as halogen carriers for producing flame-resistant foams. However, it is very difficult to dissolve these bis-ethers in such hydroxyl compounds. The ether either quickly crystallizes from solutions containing it at the required concentrations or the solution solidifies to a solid crystalline paste which is no longer pourable. It is true that low-viscosity, pourable polyether derivatives of halogenated bisphenols could be obtained in accordance with U.S. Application No. 373,230 by first preparing the hydroxyl polyethers of halogen-free bisphenols in known manner and then halogenating them with elemental halogen, such as bromine. The polyethers obtained in this way have a pourable consistency and the foams produced from them, and in particular, polyisocyanurate foams, have excellent fire characteristics. However, these foams have the disadvantage that the surface tends to become brittle and the adherence to the covering layers is poor. Moreover, the procedure described in the above-mentioned U.S. application is complicated in practice because polyetherification and halogenation are two completely separate reactions each of which requires special apparatus so that they must be carried out in two separate production units. In view of the high costs of apparatus (use of corrosion-resistant apparatus, e.g. of special steel) for halogenation, it is desirable to achieve a high degree of halogenation in order to make efficient use of the apparatus. It is, therefore, more rational to use a highly halogenated starting material for producing a halogenated flame-resistant resin or its precursor than to halogenate this resin or precursor subsequently to the required, lower degree of halogenation.